The present disclosure relates to methods and apparatuses useful in characterizing the flowability of a dry powder. In particular, the methods and apparatuses are useful in characterizing the flowability of toner particles.
A typical flexible electrophotographic imaging member belt comprises at least one photoconductive insulating layer. The imaging member is imaged by uniformly depositing an electrostatic charge on the imaging surface of the electrophotographic imaging member and then exposing the imaging member to a pattern of activating electromagnetic radiation, such as light, which selectively dissipates the charge in the illuminated areas of the imaging member to create an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking toner particles on the imaging member surface. The resulting visible image can then be transferred to a suitable receiving member or substrate, such as paper.
A two-component developer or a single-component developer may be used to develop the visible image. A two-component developer may be composed of a non-magnetic toner, i.e. a toner which does not contain magnetic particles, and a magnetic carrier. The toner particles are brought into frictional contact with the carrier particles and stick to the carrier particles electrostatically. The carrier particles are then adhered to a sleeve by magnetic force and transferred to a developing region. The toner particles are carried by the carrier particles to the developing region. In contrast, a single-component developer system uses only toner, and does not include a carrier. When the toner is not magnetic, the single-component developer system is known as a non-magnetic, single-component development (NMSCD) system.
Flowability is a measure of the ease with which a loose particulate solid flows. Flowability is critical to the performance of an imaging member. In particular, toner particles of a low flowability toner tend to agglomerate. Agglomeration may lead to the visible image not being an accurate representation of the electrostatic image, with areas of the substrate receiving too much or too little toner.
Methods for measuring flowability in a two-component development system include cohesion testing, Freeman FT4 testing, and angle of repose. In cohesion testing, a plurality of mesh screens with different sized openings is arranged in a vertical stack with the screen having the largest sized openings at the top. An aerated toner is poured into the top screen. After a fixed period of time, the amount of toner in the screen with the smallest sized openings, i.e. the bottom screen, is measured. A greater mass in the bottom screen correlates to a better flowability.
In Freeman FT4 testing, a sample of toner is compressed by a known force to determine how much the volume of the toner is reduced. A lower compressibility correlates to a better flowability.
The angle of repose can be determined by pouring an aerated toner sample into a funnel and measuring the angle of the pile of toner created under the funnel. A lower angle correlates to a better flowability.
The three tests described above can be used to characterize flowability in a two-component system. However, the results of these tests do not correlate well with the flow performance observed in NMSCD systems. It would be desirable to develop methods for characterizing the flowability of a toner in a NMSCD system.